<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<input type="text" placeholder="半径" id="r">
<input type="text" placeholder="周长" id="c">
<input type="text" placeholder="面积" id="s">


<script>
    var p = prompt("请输入圆的半径");
    var c = 2*p*Math.PI;
    var s = p*p*Math.PI;


    document.querySelector("#r").value= p;
    document.querySelector("#c").value= c;
    document.querySelector("#s").value= s;

</script>

</body>
</html>